Campaign debt, Gingrich said Saturday afternoon, could factor into who former presidential candidate Rick Santorum may endorse.

Following a tour of the NASCAR museum, Gingrich said he spoke with Santorum in St. Louis, Mo. but only briefly. (This was the same day the Speaker visited the St. Louis Zoo, was nipped by a penguin and met a tiger named Callista – just like his wife, he joked to reporters.)

"I'd love to have his endorsement but he has to do what he thinks is right for his family and he has to do what … will help pay off his campaign debt,” Gingrich said. “I am not going to put any pressure on Rick but obviously I'd love to have his endorsement."

After Santorum’s exit from the GOP race, many have called on Gingrich to withdraw as well. But Gingrich says he is staying in for the Americans he meets at events who encourage him to continue running.

“I want you to know I am the last conservative standing and I am still standing and I am running hard,” Gingrich said at a Tea Party rally here. He said that remaining in the race and competing with front-runner Mitt Romney helps the Republican Party.

“I think it helps the party because it gives us the chance to outline very big solutions and to build clarity towards the fall campaign,” he said. “I think ultimately we are all going to be on the same team.”